Re: [PATCH] x86/build: fix compiler support check for CONFIG_RETPOLINE
On Wed, Dec 5, 2018 at 3:08 PM Zhenzhong Duan wrote: > > > On 2018/12/5 11:00, Masahiro Yamada wrote: > > It is wrong to add CONFIG option diagnostic to the Makefile parse > > stage. > > > > Once you are hit by the error about non-retpoline compiler, the > > compilation still breaks even after disabling CONFIG_RETPOLINE. > > > > The easiest fix is to move this check to the "archprepare" like commit > > 829fe4aa9ac1 ("x86: Allow generating user-space headers without a > > compiler") did. > > > > Link: https://lkml.org/lkml/2018/12/4/206 > > Reported-by: Meelis Roos > > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on > > compiler support") > > Signed-off-by: Masahiro Yamada > > --- > > > > arch/x86/Makefile | 14 -- > > 1 file changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > > index f5d7f41..ae0148b 100644 > > --- a/arch/x86/Makefile > > +++ b/arch/x86/Makefile > > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare > > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > > > > # Avoid indirect branches in kernel to deal with Spectre > > -ifdef CONFIG_RETPOLINE > > -ifeq ($(RETPOLINE_CFLAGS),) > > - $(error You are building kernel with non-retpoline compiler, please > > update your compiler.) > > -endif > > - KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) > > -endif > > +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) > > Is it better to also move "# Avoid indirect branches in kernel to deal > with Spectre" > > and "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)"? > > Seems unconditionaly using "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)" will > have compiler > > using "__x86_indirect_thunk_\reg" call even ifCONFIG_RETPOLINE is > disabled. I guess > > link process will fail? Good catch. I will send v2. Thanks. > Thanks > > Zhenzhong > > > > > archscripts: scripts_basic > > $(Q)$(MAKE) $(build)=arch/x86/tools relocs > > @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO > > @echo Compiler lacks asm-goto support. > > @exit 1 > > endif > > +ifdef CONFIG_RETPOLINE > > +ifeq ($(RETPOLINE_CFLAGS),) > > + @echo "You are building kernel with non-retpoline compiler." >&2 > > + @echo "Please update your compiler." >&2 > > + @false > > +endif > > +endif > > > > archclean: > > $(Q)rm -rf $(objtree)/arch/i386 -- Best Regards Masahiro Yamada
Re: [PATCH] x86/build: fix compiler support check for CONFIG_RETPOLINE
On 2018/12/5 11:00, Masahiro Yamada wrote: It is wrong to add CONFIG option diagnostic to the Makefile parse stage. Once you are hit by the error about non-retpoline compiler, the compilation still breaks even after disabling CONFIG_RETPOLINE. The easiest fix is to move this check to the "archprepare" like commit 829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler") did. Link: https://lkml.org/lkml/2018/12/4/206 Reported-by: Meelis Roos Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support") Signed-off-by: Masahiro Yamada --- arch/x86/Makefile | 14 -- 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index f5d7f41..ae0148b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -fno-asynchronous-unwind-tables # Avoid indirect branches in kernel to deal with Spectre -ifdef CONFIG_RETPOLINE -ifeq ($(RETPOLINE_CFLAGS),) - $(error You are building kernel with non-retpoline compiler, please update your compiler.) -endif - KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -endif +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) Is it better to also move "# Avoid indirect branches in kernel to deal with Spectre" and "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)"? Seems unconditionaly using "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)" will have compiler using "__x86_indirect_thunk_\reg" call even ifCONFIG_RETPOLINE is disabled. I guess link process will fail? Thanks Zhenzhong archscripts: scripts_basic $(Q)$(MAKE) $(build)=arch/x86/tools relocs @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO @echo Compiler lacks asm-goto support. @exit 1 endif +ifdef CONFIG_RETPOLINE +ifeq ($(RETPOLINE_CFLAGS),) + @echo "You are building kernel with non-retpoline compiler." >&2 + @echo "Please update your compiler." >&2 + @false +endif +endif archclean: $(Q)rm -rf $(objtree)/arch/i386
Re: [PATCH] x86/build: fix compiler support check for CONFIG_RETPOLINE
On Wed, Dec 5, 2018 at 12:23 PM Zhenzhong Duan wrote: > > Hi Masahiro, > > > Thanks for fixing. > There is a question still confusing me. There are many CONFIG_* used in > arch/x86/Makefile. > Will they also be impacted or not? The top level Makefile (and arch/*/Makefile) is getting huge. Parsing the whole Makefile everytime means, it computes variables that may or may not be used. $(call cc-option,...) is a bit costly, but other parts are unnoticeable in terms of performance. I am addressing the use of $(error ...) / $(warning ...) in the non-recipe context since they could break the build for false positive reasons. > # grep CONFIG_ arch/x86/Makefile > ifeq ($(CONFIG_X86_32),y) > cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8) > cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona) > .. > drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/ > drivers-$(CONFIG_PCI) += arch/x86/pci/ > drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/ > drivers-$(CONFIG_PM) += arch/x86/power/ > drivers-$(CONFIG_FB) += arch/x86/video/ > ifeq ($(CONFIG_X86_DECODER_SELFTEST),y) > > Thanks > Zhenzhong > On 2018/12/5 11:00, Masahiro Yamada wrote: > > It is wrong to add CONFIG option diagnostic to the Makefile parse > > stage. > > > > Once you are hit by the error about non-retpoline compiler, the > > compilation still breaks even after disabling CONFIG_RETPOLINE. > > > > The easiest fix is to move this check to the "archprepare" like commit > > 829fe4aa9ac1 ("x86: Allow generating user-space headers without a > > compiler") did. > > > > Link: https://lkml.org/lkml/2018/12/4/206 > > Reported-by: Meelis Roos > > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on > > compiler support") > > Signed-off-by: Masahiro Yamada > > --- > > > > arch/x86/Makefile | 14 -- > > 1 file changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > > index f5d7f41..ae0148b 100644 > > --- a/arch/x86/Makefile > > +++ b/arch/x86/Makefile > > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare > > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > > > > # Avoid indirect branches in kernel to deal with Spectre > > -ifdef CONFIG_RETPOLINE > > -ifeq ($(RETPOLINE_CFLAGS),) > > - $(error You are building kernel with non-retpoline compiler, please > > update your compiler.) > > -endif > > - KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) > > -endif > > +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) > > > > archscripts: scripts_basic > > $(Q)$(MAKE) $(build)=arch/x86/tools relocs > > @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO > > @echo Compiler lacks asm-goto support. > > @exit 1 > > endif > > +ifdef CONFIG_RETPOLINE > > +ifeq ($(RETPOLINE_CFLAGS),) > > + @echo "You are building kernel with non-retpoline compiler." >&2 > > + @echo "Please update your compiler." >&2 > > + @false > > +endif > > +endif > > > > archclean: > > $(Q)rm -rf $(objtree)/arch/i386 -- Best Regards Masahiro Yamada
Re: [PATCH] x86/build: fix compiler support check for CONFIG_RETPOLINE
Hi Masahiro, Thanks for fixing. There is a question still confusing me. There are many CONFIG_* used in arch/x86/Makefile. Will they also be impacted or not? # grep CONFIG_ arch/x86/Makefile ifeq ($(CONFIG_X86_32),y) cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8) cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona) .. drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/ drivers-$(CONFIG_PCI) += arch/x86/pci/ drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/ drivers-$(CONFIG_PM) += arch/x86/power/ drivers-$(CONFIG_FB) += arch/x86/video/ ifeq ($(CONFIG_X86_DECODER_SELFTEST),y) Thanks Zhenzhong On 2018/12/5 11:00, Masahiro Yamada wrote: It is wrong to add CONFIG option diagnostic to the Makefile parse stage. Once you are hit by the error about non-retpoline compiler, the compilation still breaks even after disabling CONFIG_RETPOLINE. The easiest fix is to move this check to the "archprepare" like commit 829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler") did. Link: https://lkml.org/lkml/2018/12/4/206 Reported-by: Meelis Roos Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support") Signed-off-by: Masahiro Yamada --- arch/x86/Makefile | 14 -- 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index f5d7f41..ae0148b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -fno-asynchronous-unwind-tables # Avoid indirect branches in kernel to deal with Spectre -ifdef CONFIG_RETPOLINE -ifeq ($(RETPOLINE_CFLAGS),) - $(error You are building kernel with non-retpoline compiler, please update your compiler.) -endif - KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -endif +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) archscripts: scripts_basic $(Q)$(MAKE) $(build)=arch/x86/tools relocs @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO @echo Compiler lacks asm-goto support. @exit 1 endif +ifdef CONFIG_RETPOLINE +ifeq ($(RETPOLINE_CFLAGS),) + @echo "You are building kernel with non-retpoline compiler." >&2 + @echo "Please update your compiler." >&2 + @false +endif +endif archclean: $(Q)rm -rf $(objtree)/arch/i386
[PATCH] x86/build: fix compiler support check for CONFIG_RETPOLINE
It is wrong to add CONFIG option diagnostic to the Makefile parse stage. Once you are hit by the error about non-retpoline compiler, the compilation still breaks even after disabling CONFIG_RETPOLINE. The easiest fix is to move this check to the "archprepare" like commit 829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler") did. Link: https://lkml.org/lkml/2018/12/4/206 Reported-by: Meelis Roos Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support") Signed-off-by: Masahiro Yamada --- arch/x86/Makefile | 14 -- 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index f5d7f41..ae0148b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -fno-asynchronous-unwind-tables # Avoid indirect branches in kernel to deal with Spectre -ifdef CONFIG_RETPOLINE -ifeq ($(RETPOLINE_CFLAGS),) - $(error You are building kernel with non-retpoline compiler, please update your compiler.) -endif - KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -endif +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) archscripts: scripts_basic $(Q)$(MAKE) $(build)=arch/x86/tools relocs @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO @echo Compiler lacks asm-goto support. @exit 1 endif +ifdef CONFIG_RETPOLINE +ifeq ($(RETPOLINE_CFLAGS),) + @echo "You are building kernel with non-retpoline compiler." >&2 + @echo "Please update your compiler." >&2 + @false +endif +endif archclean: $(Q)rm -rf $(objtree)/arch/i386 -- 2.7.4